The operation is being viewed as a decisive push against Daesh in Raqqa where civilians have endured the brutal rule of the terrorist group since 2014.

Syrian Arab fighters have announced they are walking away from an operation to retake the Syrian city of Raqqa from Daesh

The decision by the Raqqa Revolutionary Brigade, or Liwa Thuaar Raqqa, would leave the offensive to the YPG, which is the Syrian branch of the PKK. The PKK, which has been behind a 40-year insurgency in Turkey, seeks to carve out a separate Kurdish state in the region.

Turkey deems the PKK and its affiliates to be terrorists and says it won't allow the YPG to form a corridor across its southern border in northern Syria. Despite the EU and the US also listing the PKK as a terrorist organisation, they treat the YPG as a separate group.

The announcement of the Syrian Arab brigade comes after the YPG broke an agreement that stated only Arabs would lead the charge to capture the Daesh stronghold. Both are part of the US-backed Syrian Democratic Forces (SDF).

Most of the civilians in Raqqa are Arabs and there have been concerns that the YPG's involvement may complicate the situation.

"YPG did not keep to what we had agreed – that the battle be led by the brigade and that the fighters all come from Raqqa itself," said Mahmoud Hadi, a senior Brigade leader, according to Middle East Eye.

The Raqqa Revolutionary Brigade says it's the only Arab force taking part in the offensive dubbed "Euphrates Wrath" that began on November 6.

Turkey, a NATO member, has been against the involvement of the YPG in the offensive that Washington hopes would be decisive in weakening Daesh in Syria.

The SDF offensive on Raqqa started despite Turkey's opposition. But Washington agreed not to equip the militia with heavy weapons like artillery and anti-tank missiles, according to The Economist.

Hadi said the Arab fighters were being sidelined on the beset of Washington.

"The agreement was that the YPG would only provide logistical support for the operation," he said.

"Everything had been agreed beforehand, we even agreed which flags would be raised. But what happened on the ground has unfortunately been the complete opposite to what we had agreed."

Despite opting out of the battle, he said, the brigade remains part of the SDF.

This is a complete opposite to US's stated position.

"(The operation needs) a predominantly Arab and Sunni Arab force," said Chairman of the US Joint Chiefs of Staff General Joseph Dunford during his meeting with Turkish counterpart Hulusi Akar on Sunday.

The operation should be led by local tribes and other people from the vicinity of Raqqa, he said.

A day after the start of Raqqa offensive, Turkey's Deputy Prime Minister Numan Kurtulmus said US must realise the importance of involving legitimate players in fight against Daesh.

"We tell them that all unnecessary steps taken by non-Arab forces in Raqqa will end up being to the disadvantage of America as well. It would also be against regional peace, a dead end, a wrong path."

Daesh claims Raqqa to be the capital of its self-proclaimed caliphate in Syria.